The present invention relates to a sulphidized catalyst which contains platinum on activated carbon and a process for its preparation.
Sulphidized catalysts which contain noble metals have been prepared on a large scale and used for decades. A process for preparing this type of catalyst is described, for example, in DE-PS 21 50 220. A higher selectivity for the desired chemical reaction, generally with reduced catalyst activity, is produced by partial poisoning of the catalyst, by sulphidizing the catalyst which contains a noble metal with a compound which contains sulphur. Little is known about the sulphidizing mechanism itself, the nature of the sulphur bonded to the catalyst surface or the interactions between sulphur, noble metal and support.
For selective hydrogenation of halogenated nitroaromatic compounds (see, for example, prior printed German patent application P 42 18 866.0) and reductive alkylation (DE-OS 2736228), in particular, catalysts containing platinum as the noble metal and activated carbon as the support are preferred above all other catalyst systems.
The selectivity of these catalysts in these reactions is improved by partial poisoning by means of sulphidization.
Sulphur itself or other sulphur-containing compounds, such as H.sub.2 S, dimethyl sulphoxide, (NH.sub.4).sub.2 S, Na.sub.2 S, Na.sub.2 SO.sub.4, are used as sulphidizing agents, wherein, e.g., the sulphur is released from the sulphur-containing compound by the action of a strong acid, such as H.sub.2 SO.sub.4. In this case, concentrations of 0.1-10 moles of sulphur per mole of platinum, but preferably 0.1-2 moles of sulphur per mole of platinum, are used.